Mechanisms for cellular, hormonal and viral regulation of plasma membrane transport systems in mouse fibroblast cultures will be investigated. In order to understand the physiological and functional significance of protein kinase phosphorylation of plasma membrane proteins in nontransformed 3T3 mouse fibroblast cultures and their Simian Virus 40 or chemically-transformed derivatives, transport systems for ions and nutrients will be surveyed for functional linkage to membrane protein phosphorylation using intact cells and their isolated plasma membrane vesicles which catalyze transport. The feasibility of extending the methodology and tactics developed using this model system to rat mammary epithelial cell cultures will be tested, as an approach to investigate the possible relationship of specific hormonal stimuli to membrane phosphorylation, and the effect of phosphorylation on surface membrane hormone receptor activities and specialized transport and secretory functions expressed in these differentiated cell cultures.